Pneumatically operated braking systems for trucks, trailers and the like, typically feature air pressure activated brake chambers, which are utilized to move movable brake system pushrods which typically extend perpendicularly outwards from the air pressure chambers. These system also typically include a slack adjuster lever and a clevis pin for pivoting and mounting the slack adjuster on a pushrod yoke. In use, when the brake pedal is depressed, air pressure moves the pushrod outwards, which moves the slack adjuster, in an arc travel configuration, and thus turning a cam which ultimately actuates the brakes.
Over time, as the brakes are repeatedly applied, the distance traveled by the pushrod may increase, by for example, wear or improper maintenance, and thus the system requires regular inspection of the push rod travel distance to ensure that the brakes are operating within pre-established parameters, and are operating in good working order. To emphasize the importance of checking the brake pushrod movement, regular inspection of the pushrod travel distance is often required by regulatory authorities, and thus, inspection can be mandatory.
There have been attempts to facilitate this mandatory brake stroke inspection with the use of inspection apparatuses that have a bracket and attached start point and travel end point indicators, fastened to the brake chamber or a component of the brake system.
By way of example of these types of devices, U.S. Pat. No. 4,279,214 issued Jul. 21, 1981, discloses a brake adjustment indicator which can be installed on a vehicle with pneumatic brakes. The indicator includes a sleeve that loosely fits over the push rod of a pneumatic actuator.
U.S. Pat. No. 4,776,438 issued Oct. 11, 1988, discloses a brake adjustment indicator which includes a mounting bracket having an elongated body with a slot that runs parallel to a rod that extends through an air brake chamber and connects at one end to the brake arm by a clevis pin.
U.S. Pat. No. 4,879,964 issued Nov. 14, 1989, discloses an air brake adjustment marker that includes an air supply, an air canister, and moveable members that include a push rod that extends from the air canister and has a first extended position and a second over-extended position. The adjustment marker includes a chain attached to the push rod, and an indicator flag that is activated when the push rod is in the over-extended position.
U.S. Pat. No. 5,244,061 issued Sep. 14, 1993, discloses an air brake stroke length gauge that operates in conjunction with an air brake system. The gauge comprises of a stroke length indicator that is mounted on the push rod, and a reference marker that is attached to the air brake system at a distance which corresponds to the appropriate stroke length for the brake system when properly adjusted.
U.S. Pat. No. 5,320,198 issued Jun. 14, 1994, discloses a indicator for indicating the setting and linear stroke movement of a brake rod of a brake assembly. The gauge includes reference indicators that are located on both the brake rod's clevis and on the arm of the brake's slack adjustment member, thereby indicating the brake rod travel and the need for brake adjustment.
U.S. Pat. No. 5,441,128 issued Aug. 15, 1995, discloses a bracket body that can be attached to a brake rod and to the clevis member of a conventional brake adjustment apparatus. The bracket body provides for an indirect measurement of the brake rod travel and adjustment.
U.S. Pat. No. 5,699,880, issued Dec. 23, 1997, discloses the use of a brake adjustment indicator including a mounting bracket, having an elongated body with a slot, and a spacer for receiving two bolts for indicating limit positions.
Finally, U.S. Pat. No. 5,913,385, issued Jun. 22, 1999, shows the use of a brake adjustment indicator having a clevis pin that provides a visual indication of brake pushrod travel during use, in relation to two indicator posts.
While useful, these apparatuses are somewhat limited in that they typically require pressure to be applied to the brakes each time an inspection is undertaken, so that the maximum travel of the pushrod can be directly observed. However, use of these devices by an operator will require either a brake pedal jamming device that can be wedged into place to apply pressure on the brake pedal, or requires a second person to hold the brake pedal down so that the pushrod stroke travel can be visually inspected. These approaches are not always convenient, and therefore, not always done on a regular basis.
Also, it can be noted that operators may attempt to use the parking brakes as a means of applying the brakes for inspection but this approach is not satisfactory since a parking brake application will typically use less force than a full brake application and thus may show a false reading of actual pushrod travel.
Moreover, a full inspection might require two sets of visual inspections, since it will also be necessary to observe the pushrod position when the brakes are not applied, in order to establish that the brake pushrod initial position (without the brakes being applied), is at an appropriate position, and therefore, will be conducive for the pushrods to move, and the brakes to operate, within normal expected tolerances.
To overcome these difficulties, it would be advantageous to provide an easily implemented approach to showing the maximum pushrod travel distance, without needing a second person's assistance, or in face, even applying the brakes during the inspection process. It would also be advantageous to be able to observe the initial brake pushrod position, as well as the maximum pushrod travel position, in a single inspection.